1. Field of the Invention
The present invention pertains to the field of high strength elastomers. More particularly, the present invention pertains to high strength elastomers suited for use in high temperature shear ply applications, such as for transferring loads from the pressure vessel of either a stand-alone composite rocket motor or strap-on composite booster to a rocket skirt.
2. Description of Related Art
Although there are many variations to the configuration and construction of a rocket motor, rocket motors generally comprise an outer motor casing for housing an energetic fuel or propellant. In the case of a solid rocket motor, the outer motor casing houses a solid propellant formulated to undergo combustion while contributing to the production of adequate thrust for attaining propulsion of the rocket motor. Other types of rocket motors, such as hybrid, reverse-hybrid motors, and bi-liquid motors, make use of a liquid oxidizer and/or liquid fuel. A rubber insulation layer and a liner positioned between the casing and the propellant serve to protect the rocket motor casing from high temperature combustion products generated as the propellant burns.
Rocket motor casings are generally made of metal, a composite material, or a combination of metal and composite materials. Composite materials are typically prepared by winding a resin-impregnated fiber on a mandrel to shape the rocket motor casing. The resin may be a curable resin, and is normally either an epoxy or phenolic resin. The fibers are usually carbon graphite fibers or aramid fibers.
The aft end portion of the rocket motor casing is directed to a rocket skirt. Typically, an outer surface portion of a composite rocket motor casing is covered with a shear ply layer for coupling the rocket motor casing to the skirt. High strength rubber compositions are often used for the forming shear ply layers that connect the rocket skirt with the composite rocket motor casing.
Silica-filled nitrile polybutadiene rubber (NBR) compositions are presently used to form shear ply layers that connect a rocket skirt with a stand-alone composite rocket motor casing. The conventional NBR compositions have been found generally to exhibit a tensile strength and ultimate elongation on the order of 20,684 kPa (3000 psi) and 700 percent, respectively. Although these properties are adequate for stand-alone motor applications, new developments in rocketry call for the use of strap-on boosters across a wide temperature range. The strap-on design imparts higher loads to the shear ply than a stand-alone rocket motor. These higher load designs encountered in strap-on booster applications have created a perceived need for a novel shear ply material that possesses a higher tensile strength and improved high temperature properties compared to conventional silica-filled NBR compositions.
It is therefore one of the objects of this invention to provide a precursor composition that, upon curing, forms a high strength rubber that can have sufficient flexion, strength, and high temperature properties for use, by way of example, in a shear ply for rocketry applications.
Another object of the invention is to provide a rubber material that may have sufficient flexion, strength, and high temperature properties for use in a shear ply for rocketry applications. It is especially preferred by this object that the rubber material have a tensile strength and ultimate elongation that are sufficient for the intended preferred application of a shear ply.
It is another object of this invention to provide a rocket motor assembly comprising a shear ply constructed and arranged for transferring loads between a coupled casing and skirt of the rocket motor assembly.
Yet another object of the invention is to provide corresponding methods for making the high strength rubber material from the precursor composition, as well as methods of making and applying shear ply articles using the high strength rubber composition.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, according to one aspect of this invention there is provided a precursor composition that is curable into a rubber component and comprises:
(a) a first hydrogenated nitrile conjugated-diene copolymer modified by a metal salt unsaturated carboxylic acid ester, wherein the hydrogenated nitrile conjugated-diene copolymer is derived from a first composition comprising a first ethylenically unsaturated nitrile and a first conjugated diene;
(b) a second hydrogenated nitrile conjugated-diene copolymer derived from a second composition comprising a second ethylenically unsaturated nitrile and a second conjugated diene; and
(c) a curing agent,
wherein (a) and (b) are intermixed.
In accordance with another aspect of this invention, there is provided a rubber component formed from the precursor composition.
In accordance with still another aspect of this invention, a method is provided in which components (a) and (b) of the precursor composition are mixed together to form a blend, and the blend is cured with a curing agent, such as a peroxide curing agent, to form the rubber component.
In accordance with a further aspect of this invention, there is provided a method for coupling a skirt to a composite rocket motor case of a rocket motor engine. This aspect of the invention involves providing a rubber shear ply comprising the rubber component of this invention, and interposing the rubber shear ply between a skirt and a composite rocket motor case of a rocket motor assembly.
The present invention overcomes the problems that are outlined above, addresses the above and other objects, and advances the art by providing a high strength rubber composition having improved strength across a broad temperature range for use in various applications. These applications include, but are not limited to, rocketry applications, especially in the context of forming shear ply layers. As used herein, the term xe2x80x9crubberxe2x80x9d is defined to encompass both synthetic and natural elastomers. The rubber composition, in its various embodiments and methodologies, can facilitate the use of stronger rocket motors, as well as new types of motors.